X-ray device for tomosynthesis

ABSTRACT

The invention relates to an X-ray device for the formation of slice images of an object ( 4 ) to be examined, which device includes an X-ray source ( 1 ), an X-ray detector ( 2 ), a transport device ( 3 ) for moving the object ( 4 ) to be examined during the acquisition of a series of X-ray projection images of the object ( 4 ) in a movement plane (B) that is situated parallel to the imaging plane (A), and also includes a control device ( 5 ) for controlling the acquisition of the X-ray projection images and the transport device ( 3 ), slice images of the object ( 4 ) to be examined being formed from the X-ray projection images by means of a tomosynthesis method. In order to enable the formation of slice images of large objects to be examined, or of large parts thereof, within an as short as possible period of time, in accordance with the invention the X-ray source ( 1 ) and the X-ray detector ( 2 ) are arranged so as to be statical during the acquisition of the X-ray projection images and the control device ( 5 ) is configured in such a manner that the speed of motion of the object ( 4 ) to be examined and the instants of acquisition of the X-ray projection images are such that all points to be examined in an examination zone of the object ( 4 ) to be examined are imaged in at least 10, but preferably in at least 50 different X-ray projection images.

[0001] The invention relates to an X-ray device for the formation of slice images of an object to be examined, which device includes an X-ray source, an X-ray detector, a transport device for moving the object to be examined during the acquisition of a series of X-ray projection images of the object to be examined in a movement plane that is situated parallel to the imaging plane, and also includes a control device for controlling the acquisition of the X-ray projection images and the transport device, slice images of the object to be examined being formed from the X-ray projection images by means of a tomosynthesis method. The invention also relates to a corresponding method of forming slice images of an object to be examined.

[0002] The formation of slice images by means of tomosynthesis has been known since long. The X-ray source and the X-ray detector are then moved in opposite directions in parallel planes for the acquisition of X-ray projection images of an object to be examined that is arranged between said planes. Such a movement is performed in such a manner that the projection line between the X-ray source and the X-ray detector, that is, the connecting line between the focal point of the X-ray source and the center of the X-ray detector, extends through the same point of the object to be examined for each X-ray projection image. Different slice images can then be formed by simple addition of the image values that are associated with a voxel of a slice to be imaged of the object to be examined in different X-ray projection images. The object to be examined itself is not moved during the acquisition of the X-ray projection images.

[0003] DE 197 56 697 A1 discloses a device for X-ray tomosynthesis of parcels. Therein, a parcel is moved linearly through an X-ray system by means of a transport device; this X-ray system includes at least three X-ray scanning units whose fan beams are configured in such a manner that the parcel is simultaneously irradiated at different angles.

[0004] According to the known method in all cases only the examination of a very limited part of the object to be examined is possible. For the examination and the formation of slice images of large objects, such a known method must be carried out several times in different regions of the object to be examined, after which the separately formed slice images can be combined, if desired. However, it is desirable to enable the inspection of large areas of the object to be examined merely by way of a single execution of the method and to form slice images of a large area within the shortest possible period of time, for example, the formation of whole body slice images of a patient or slice images of large pieces of luggage in the case of a luggage inspection application.

[0005] Therefore, it is an object of the invention to provide an X-ray device and a method that have been improved in a sense that slice images of large examination zones can also be formed within a short period of time.

[0006] On the basis of an X-ray device of the kind set forth and a method of the kind set forth this object is achieved in that the X-ray source and the X-ray detector are arranged to be statical during the acquisition of the X-ray projection images and that the control device is configured in such a way that the speed of the motion of the object to be examined and the instants of acquisition of the X-ray projection images are chosen to be such that all points to be imaged in an examination zone of the object to be examined are imaged in at least 10, but preferably in at least 50 different X-ray projection images.

[0007] The invention is based on the recognition of the fact that it is advantageous to move the object to be examined, that is, the patient or the piece of luggage to be inspected, instead of the X-ray source and the X-ray detector during the acquisition of the X-ray projection images. The instants of acquisition of the X-ray projection images and the speed of movement of the object to be examined are then optimized for the relevant tomosynthesis method, preferably being of the digital type in the present case, in such a manner that each point of the examination zone to be imaged in the object to be examined appears in at least a minimum number of X-ray projection images, said minimum number amounting to at least 10, but preferably to at least 50 or even from 100 to 200, so as to achieve an adequate image quality. This number, however, is dependent to a high degree on the type, on the condition and on the size of the object to be examined. This makes it possible to form slice images also of large objects after a single execution of the method in accordance with the invention, for example, whole body slice images of a patient as they are necessary for trauma scanning. Moreover, the X-ray device and the method in accordance with the invention can also be used for the testing of materials and for the inspection of luggage; integration in an existing processing chain is then also possible.

[0008] In order to optimize the tomosynthesis angle, that is, the angle of aperture of the X-ray beam that emanates from the X-ray source so as to traverse the object to be examined and be incident on the X-ray detector, the distance between the X-ray source and the X-ray detector can be varied in one embodiment in accordance with the invention. It should notably be possible to adapt the position of the X-ray source in a direction that is situated perpendicularly to the detector plane, corresponding to the imaging plane, while the X-ray detector is arranged so as to be statical. Consequently, the tomosynthesis angle can be optimized in such a manner that the image quality is optimized. The larger the tomosynthesis angle, the better the image quality will be. The position of the X-ray source, however, preferably is not changed during the acquisition of the X-ray projection images.

[0009] In a further preferred embodiment at least two series of X-ray projection images are acquired while the X-ray source occupies a different position each time. Preferably, the X-ray source is then asymmetrically arranged relative to the detector, that is, for example, in such a manner that it faces the left edge zone of the detector during the acquisition of the first series and the right edge zone of the detector during the acquisition of the second series. This embodiment enables a further optimization of the tomosynthesis angle and hence of the image quality.

[0010] The tomosynthesis angle can be optimized even further by means of at least one further X-ray detector that is included in a further embodiment of the invention and is arranged adjacent the first X-ray detector.

[0011] Preferably, in accordance with the invention the transport device is moved at an irregular speed and in different, changing directions for the acquisition of the X-ray projection images. It has been found that the formation of artefacts in the slice images can be reduced or even avoided when the object to be examined is not rectilinearly and continuously moved at the same speed through the X-ray beam during the acquisition of the X-ray projection images, but is moved in a kind of “chaotic” way while the speed and the direction of movement change continuously. It may even be advantageous to move the transport device manually and completely irregularly, because the fewest imaging defects and artefacts then occur.

[0012] Further advantageous embodiments are disclosed in the dependent claims. It is to be noted that the method for the formation of slice images in accordance with the invention may be elaborated in an identical or similar way as and may be realized in versions as described above for the X-ray device in accordance with the invention and as disclosed in the dependent claims that relate to the claim 1.

[0013] The invention will be described in detail hereinafter with reference to the drawings. Therein:

[0014]FIG. 1 is a diagrammatic representation of an X-ray device in accordance with the invention, and

[0015]FIG. 2 shows a further embodiment of an X-ray device in accordance with the invention.

[0016] The X-ray device that is shown in FIG. 1 is provided with an X-ray source 1 and a preferably flat, two-dimensional X-ray detector 2 (which may also be an image intensifier) wherebetween a patient 4 is arranged on a transport device 3, being a patient table in the present case. The transport device 3 with the patient 4 is moved in the plane of motion B, that is, in the x direction and/or the y direction for the acquisition of X-ray projection images, so that the conical X-ray beam 6 successively traverses different regions of the patient 4, said regions then being imaged in the imaging plane A on the X-ray detector 2. The motion of the patient 4 is then controlled, like the X-ray source 1 and the X-ray detector 2, by a control device 5. The X-ray source 1 and the X-ray detector 2 are arranged so as to be statical for the acquisition of the X-ray projection images. However, the position of the X-ray source 1 can be varied in the z direction in order to optimize the tomosynthesis angle α.

[0017] The image quality of the slice images formed by means of tomosynthesis is then dependent essentially on the tomosynthesis angle α and on the number n of X-ray projection images that is formed during the data acquisition for a point to be imaged in the examination zone. The tomosynthesis angle α results from the width w=2w_(d) of the detector 2 and the distance d=d_(t)+d_(p) between the detector 2 and the X-ray source 1 as:

α=2 tan⁻¹ (w _(d) /d).

[0018] The number n of projection images results from the time t_(b) during which the point to be imaged is situated within the X-ray beam and from the image rate f_(r) of the detector as:

n=f _(r) t _(b).

[0019] The time t_(b) results from the speed v_(t) of the transport device and from the position z of the point along the connecting axis 7 between the X-ray source and the X-ray detector as:

t _(b)=(zw)/(dv _(t)).

[0020] The maximum speed v_(t) ^(max) is dependent on the imaging rate f_(r) and on the necessary number n of X-ray projection images and amounts to:

v _(t) ^(max)=(zwf _(r))/(dn).

[0021] This will be explained in detail hereinafter on the basis of an example. It is assumed that the maximum height d_(p) of the patient is d_(p)=50 cm and that z is defined as z=d−d_(p). The imaging rate f_(r) of the detector is assumed to be f_(r)=25 images per second, and the dimensions of the detector are assumed to be 30×40 cm. In order to achieve an adequate imaging quality, each point of the patient should be imaged at least n=100 times when the above values are assumed. The following Table contains the maximum speeds that can be used for the moving of the patient and the resultant tomosynthesis angles for a detector of the kind set forth. d [mm] W_(p)[mm] α [DEG] v_(t)[mm/s] 1200 233 19 58 1000 200 23 50 800 150 28 37.5 600 67 37 17

[0022] Because the tomosynthesis angle that can be reached is not always large enough to form high-quality tomograms or slice images, further modifications can be carried out on the described construction. For example, as is shown in FIG. 2 an asymmetrical arrangement of the X-ray source and the X-ray detector can be chosen. In order to acquire a first series of X-ray projection images, the X-ray source 1 is then arranged so as to face the right-hand edge zone 21 of the detector 2 (as shown in FIG. 2a), whereas for the acquisition of a second series of X-ray projection images the X-ray source 1 is arranged so as to face the left-hand edge zone 22 of the detector 2. The direction of movement of the transport device 3 is then inverted during the second step. The tomosynthesis angle α can be doubled when use is made of such an arrangement. It is also possible in principle to acquire more than two series of X-ray projection images in order to increase the tomosynthesis angle even further.

[0023] Instead of using a single detector, one or more further detectors may be employed so as to increase the detector area. This may be done for the configuration that is shown in FIG. 1 as well as for that shown in FIG. 2; in the latter case maximum tomosynthesis angles of between 90° (for d_(t)=100 mm) and 62° (for d_(t)=500 mm) are obtained for a configuration that consists of two detectors while tomosynthesis angles of from 107° (for d_(t)=100 mm) to 78° (d_(t)=500 mm) are obtained for a configuration that consists of four detectors.

[0024] In order to avoid the formation of artefacts, instead of using motor control for the movement of the patient during the acquisition of the projection images; it is also possible to move the patient table with the patient manually and completely irregularly, that is notably in random directions of movement; of course, all points of the patient to be imaged should then be traversed an adequate number of times by the X-ray beam.

[0025] Preferably, there are also provided means for measuring the instantaneous position of the transport device for the patient (these means are not shown in the Figures). Such means are preferably provided in the transport device itself, for example, in the form of potentiometers whose measured value is proportional to the instantaneous position of the table. Such position measurement is used for the control of the movement of the object to be examined and for the control of the instants of acquisition of the X-ray projection images.

[0026] The invention can be used not only for medical purposes but is also suitable for the testing of materials or for the inspection of luggage; for example, it can then be integrated in the manufacturing process for a conveyor belt or a transport system. 

1. An X-ray device for the formation of slice images of an object (4) to be examined, which device includes an X-ray source (1), an X-ray detector (2), a transport device (3) for moving the object (4) to be examined during the acquisition of a series of X-ray projection images of the object (4) to be examined in a movement plane (B) that is situated parallel to the imaging plane (A), and also includes a control device (5) for controlling the acquisition of the X-ray projection images and the transport device (3), slice images of the object (4) to be examined being formed from the X-ray projection images by means of a tomosynthesis method, characterized in that the X-ray source (1) and the X-ray detector (2) are arranged so as to be statical during the acquisition of the X-ray projection images and that the control device (5) is configured in such a way that the speed of motion of the object (4) to be examined and the instants of acquisition of the X-ray projection images are chosen to be such that all points to be imaged in an examination zone of the object (4) to be examined are imaged in at least 10, but preferably in at least 50 different X-ray projection images.
 2. An X-ray device as claimed in claim 1, characterized in that the speed of movement of the object (4) to be examined and the instants of acquisition of the X-ray projection images are adjusted in such a manner that all points to be imaged in an examination zone of the object (4) to be examined are imaged in from 100 to 200 different X-ray projection images.
 3. An X-ray device as claimed in claim 1, characterized in that the distance between the X-ray source (1) and the X-ray detector (2) can be varied.
 4. An X-ray device as claimed in claim 1, characterized in that at least two series of X-ray projection images are acquired so as to form slice images and that the X-ray source (1) is arranged in different positions for the acquisition of the series.
 5. An X-ray device as claimed in claim 4, characterized in that the X-ray source (1) is arranged so as to face a first edge zone (21) of the X-ray detector (2) for the acquisition of the first series and so as to face a second edge zone (22) of the X-ray detector (2) for the acquisition of the second series, the first edge zone (21) being situated so as to face the second edge zone (22).
 6. An X-ray device as claimed in claim 1, characterized in that for the acquisition of X-ray projection images at least one further X-ray detector is arranged adjacent the first X-ray detector (2).
 7. An X-ray device as claimed in claim 1, characterized in that the transport device (3) can be moved manually or by means of a motor and that there are provided means for measuring the position of the table.
 8. An X-ray device as claimed in claim 1, characterized in that for the acquisition of the X-ray projection images the transport device (3) is moved, preferably manually, at an irregular speed and in different, changing directions.
 9. A method of forming slice images of an object (4) to be examined by means of an X-ray source (1), an X-ray detector (2), a transport device (3) for moving the object (4) to be examined during the acquisition of a series of X-ray projection images of the object (4) to be examined in a movement plane (B) that is situated parallel to the imaging plane (A), and by means of a control device (5) for controlling the acquisition of the X-ray projection images and the transport device (3), slice images of the object (4) to be examined being formed from the X-ray projection images by means of a tomosynthesis method, characterized in that the X-ray source (1) and the X-ray detector (2) are arranged so as to be statical during the acquisition of the X-ray projection images and that the speed of motion of the object (4) to be examined and the instants of acquisition of the X-ray projection images are chosen in such a manner that all points to be imaged in an examination zone of the object (4) to be examined are imaged in at least 10, but preferably in at least 50 different X-ray projection images. 